Su Qingyuan entered the palace in place of her twin sister who died of illness and became Xiao Jingyuan's "White Moonlight Stand-in". On the surface, she is intellectual and elegant, and plays the role of "stand-in" to perfection, but in fact, she hides a traitor and vows to find out the cause of her sister's death - her sister's death is no accident.
Xiao Jingyuan seemed to be humorous and indulged "White Moonlight" in every possible way, but he was testing Su Qingyuan's true identity while laughing. In the harem, the imperial concubine Liu Yanji was jealous of "Bai Yueguang"'s favor, so she secretly plotted against her. She also hid the secret related to the cause of her sister's death, and gradually became darker.
When Su Qingyuan's rebellion collided with Xiao Jingyuan's temptation, and when clues about the cause of her sister's death pointed to a conspiracy deep in the palace, the substitute and the emperor gradually developed complicated feelings from rivals who were suspicious of each other. Su Qingyuan maintained her independent thinking and searched for the truth in the fog, but she didn't know that she had already fallen into a bigger situation...
